Apex beat

Maximum pulse felt on the chest during heart beat

The apex beat, also called the apical impulse, is the pulse felt at the point of maximum impulse (PMI), which is the point on the precordium farthest outwards (laterally) and downwards (inferiorly) from the sternum at which the cardiac impulse can be felt. The cardiac impulse is the vibration resulting from the heart rotating, moving forward, and striking against the chest wall during systole. The PMI is not the apex of the heart but is on the precordium not far from it. Another theory for the occurrence of the PMI is the early systolic contraction of the longitudinal fibers of the left ventricle located on the endocardial surface of this chamber. This period of the cardiac cycle is called isovolumic contraction. Because the contraction starts near the base of the left ventricle and spreads toward the apex most of the longitudinal fibers of the left ventricle have shortened before the apex. The rapidly increasing pressure developed by the shortening of these fibers causes the aortic valve to open and the apex to move outward causing the PMI. Anatomical dissection of the musculature of the apex reveals that muscle fibers are no longer longitudinal oriented but form a spiral mass of muscular tissues which may also have an effect on the ability of the apex to contract longitudinally. After the longitudinal fibers contract, the ejection of blood out of the left ventricle is accomplished by the torsional action of the circumferential muscle fibers of the left ventricle that are in the mid-portion of the ventricle and contract after the longitudinal fibers. During the longitudinal fiber contraction, the volume of the left ventricle has not changed keeping the apex in intimate contact with the chest wall allowing the ability to feel the apex move outward before the heart empties greater than 55% of its volume and the apex falling away from the chest wall.

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